The invention relates to soles for athletic shoes and to athletic shoes, and in particular to such soles and shoes used in activities involving rotation on one or both feet. These activities include court sports such as basketball and squash, and field sports such as American football, soccer and baseball.
Athletic shoes have long been known which include means for improving traction with the ground. Shoes with treads of various configurations have been used widely, especially in sports where running is involved. The soles of shoes for court sports have been provided with a variety of trend designs for enhancing traction to enable fast starting, stopping and turning. In sports such as baseball, football, soccer and the like which are played on turf, athletic shoes are conventionally provided with cleats or spikes for digging into the earth to provide the desired traction and to facilitate the rapid changing of direction.
Although known tread designs and cleats greatly improve traction, they have been the source of foot and knee injuries to many athletes. Known tread designs improve traction in all directions, and tend to hold the foot fast even when the wearer is jolted or loses his or her balance, causing forces to be absorbed by the persons's tendons, ligaments and muscles. Rigid cleats as presently known are responsible for more joint injuries in the foot and knee in football, soccer and baseball than any other cause. These injuries have been found to occur because the foot is temporarily fixed to the ground by virtue of the engagement of the cleats with the ground, and the leg is unable to absorb the shock of forces imparted to it by removal of the threatened joint from the force or by corrective anatomical realignment before injury occurs. Moreover, the knee is most often in a fixed or locked state with the ligaments and muscles of the leg holding its component parts in a generally semi-flexed condition. When the athlete makes a sudden turn or "cut", or when as in football the athlete is blocking or being blocked or being tackled or when a baseball player "rounds" a base, or a pitcher pivots as he delivers a pitch, the forces impressed on the knee and ankle joints of the leg often distort the joint axes and tear or strain ligaments--these injuries most frequently being the direct result of the fixation of the foot relative to the ground.
The problem of omnidirectional traction in treaded shoe soles as a cause of foot and leg injury has apparently neither been recognized nor addressed. Various proposals have been made for releasing a football player's cleated foot from the fixed condition when potentially dangerous forces or torques are imparted to the leg or foot. Thus, a swivel shoe has been proposed for use in football which includes a turntable rotatably mounted on the forefoot part of the shoe, the turntable carrying cleats for gripping the turf. The turntable rotates in response to the exertion of a predetermined minimum torque about its axis of rotation for the purpose of eliminating rigid cleating under deleterious force conditions. A second turntable having a beveled notch mounted for rotation on the heel of the shoe is provided for adding further mobility to the foot. The foregoing swivel shoe and a discussion of the mechanics of the foot giving rise to the injuries discussed herein can be found in "The Swivel Football Shoe: A Controlled Study" by Bruce M. Cameron, M.D. and Otho Davis in The Journal of Sports Medicine, January/February 1973, p. 16. Another swivel football shoe is disclosed in U.S. Pat. No. 3,707,047 issued Dec. 26, 1972 to Nedwick. Such shoes have not found acceptance among football players, probably because of the inherent problems of malfunctioning and unreliability associated with the movable mechanical elements incorporated in these shoes. Another football shoe intended to avoid the foregoing disadvantages but also not used for probably the same reasons noted with regard to swivel football shoes, is a football shoe disclosed in U.S. Pat. No. 3,668,792 issued June 13, 1972 to York, having a breakaway sole which is removed from the body of the shoe when predetermined transverse force is applied. Significantly, no such cleated shoes have been proposed for other sports such as baseball, where similar danger of leg injuries exist.